1. Field of the Invention
The present invention relates to a recording medium reproduction apparatus for, and a recording medium reproduction method of, reproducing a data including high efficiency-encoded audio data recorded on a medium.
2. Description of the Related Art
As high efficiency-encoding system of audio data there have been standardized MPEG1 (Moving Picture Image Coding Expert Group), MPEG2, etc. MPEG1 audio comprises audio data of two channels, and MPEG2 audio is obtained by extending the MPEG1 audio so as to be applied to a multi-channel and a multi-lingual audio.
FIG. 3 is a view illustrating a frame structure of the MPEG2 audio. As illustrated in FIG. 3, a frame of MPEG2 audio comprises a MPEG1 header 1, MPEG1 audio data 2, a multi-channel header 3, multi-channel audio data 4, multi-lingual audio data 5, and a MPEG1 auxiliary data 6. The MPEG1 audio data 2 is for monaural or stereo system. The multi-channel audio data 4 is for a surround system, which comprises maximum 3.1 channels of stereo surround (2 ch), center (1 ch), and sub-woofer (0.1 ch). Further, the multi-lingual audio data 5 is audio data to deal with a variety of languages, and may have a maximum of 7 channels. The frame structure of the MPEG1 audio comprises a MPEG1 header, MPEG1 audio data, and MPEG1 auxiliary data.
Some reproduction apparatuses, each for a medium on which a plurality of audio streams high efficiency-encoded with the MPEG1, the MPEG2, etc. have been recorded, have a function of selecting two streams and mixing and outputting them. In such a reproduction apparatus, from a medium on which a background sound stream of a moving picture, for example, and sound streams expressed by a plurality of languages have been recorded, the background sound stream and the sound stream of one language are selected, mixed and output.
Thereupon, in the case of the audio stream encoded with the MPEG1, audio data of the selected two streams are decoded through separate decoders, and decoded data are mixed to provide audio outputs. Accordingly, two decoders and one mixer circuit are necessary.
In contrast, in the case of the audio stream encoded with the MPEG2, multi-lingual audio data are allowed to have 7 channels as a standard, and a decoder applied to the MPEG2 audio has a mixing function therein, so that only one decoder is needed to satisfy the foregoing requirement. This is, however, actually impossible. The reason is as follows.
The maximum bit rate of the MPEG1 audio and the MPEG2 audio is 384 kbps, and hence the total of the MPEG1 audio data, multi-channel audio data, and multi-lingual audio data should fall within 384 kbps. However, because 96 kbps or higher are required for each channel in view of a sound quality, from one stream of the MPEG2 audio, the MPEG1 audio data and the multi-lingual audio data are selected, respectively, only as 192 kbps stereo data. These two stereo data correspond to a background sound and a sound of one language, so that a multi-lingual audio cannot be realized. There is a method to record a stream composed of the same background sound and a different language on a plurality of media and to reproduce one stream upon reproduction, so as to realize a multi-lingual audio. The method however causes redundancy to be increased in proportional to the number of the streams because of the background sound being the same.
For this reason, even in the case of the MPEG2 audio, a method has been applied in which two streams are selected, and audio data of these streams are decoded, mixed through separate decoders, and output. Thus, two decoders and one mixer circuit are essential.
For instance, data recorded on a medium is assumed to be an assembly of units, each unit being composed of a header 11, audio data 12 and video data 13, as illustrated in FIG. 4. The audio data 12 and the video data 13 are high efficiency compression-encoded data encoded according to the MPEG standard or the like. The audio data 12 comprises a plurality (m) of sound streams (#0, . . . , #m) 14, each sound stream 14 being composed of a plurality (n) of continuous sound frames (#0, #1, . . . , #n) 15. The sound frame 15 comprises a frame header 16 and frame data 17.
FIG. 6 is a block diagram illustrating the structure of an optical disk reproduction apparatus for reproducing the data recorded on the optical disk. In FIG. 6, numeral 101 denotes the optical disk on which data is recorded with a structure illustrated in FIG. 4. Numeral 102 denotes an optical pickup for reading a signal recorded on the optical disk 101. The signal read by the optical pickup 102 is amplified in an RF amplifier 103 and is thereafter supplied to an RF signal processing circuit 104. The RF signal processing circuit 104 subjects the amplified signal to waveform equalization and binarization to obtain data. Binary data output from the RF signal processing circuit 104 is transmitted to a data processor 105 where the data is subjected to demodulation and error correction.
The output of the RF amplifier 103 is also transmitted to a servo control circuit 106. The servo control circuit 106 detects tracking errors and focusing errors from the output of the RF amplifier 103, and outputs both detection signals to a driving circuit 107. On the basis of both detection signals, the driving circuit 107 drives a feeding mechanism (not shown) of the optical pickup 102 for focusing control and tracking control. The servo control circuit 106 frequency-divides a synchronizing signal component extracted from the output of the RF amplifier 103, and transmits a frequency-divided signal to the driving circuit 107. The driving circuit 107 drives a disk motor 108 based upon the frequency-divided signal.
In contrast, the data subjected to the demodulation and error correction in the data processor 105 is transmitted to a system processor 109 on a data unit basis. The system processor 109 separates audio data and video data from the input data unit, and outputs the video data to an MPEG video decoder 110. The system processor 109 selects two streams among m sound streams of the audio data from the input unit data, and outputs one of the two streams to a first MPEG audio decoder 111, and the other of the same to a second MPEG audio decoder 112.
The MPEG video decoder 110 decodes the video encoded data and outputs the decoded video data to a video encoder 113. The video encoder 113 generates and outputs a video signal for reproduction from the decoded video data.
In contrast, the MPEG audio decoders 111 and 112 decode audio data for each sound frame that constitutes each sound stream, and outputs the decoded audio data to a mixer circuit 114. The mixer circuit 114 mixes the two audio data, and outputs the mixed audio data to a D/A converter 115. The mixed audio data is converted to an analog signal by the D/A converter 115, and is thereafter output through an amplifier 116 as a reproduction audio signal.
In the conventional reproduction apparatus for a medium on which a plurality of high efficiency-encoded sound streams have been recorded, two streams are selected, mixed, and output, and thereupon two decoders and one mixer circuit are required as described above. The conventional reproduction apparatus thus suffers from a problem of its being expensive.